The present invention relates to a document feed device adapted to be used in a typewriter, printer, electronic data processing equipment, etc., and provided with a pin tractor assembly which intermittently or continuously transports a document formed of a sheetlike material, e.g., printing paper, and having longitudinally spaced perforations on either side, past a printing position or work station.
In document feed devices of this type, a pin tractor member bears thereon a number of feed pins which engage perforations of a flexible sheet of material. The sheet of material is fed forward or backward in its longitudinal direction as the pin tractor member rotates.
These devices are disclosed in, for example, U.S. Pat. Nos. 2,825,559, 4,022,365 and 4,162,032.
The pin tractor member, in conjunction with a body member nonrotational relative thereto, constitutes the pin tractor assembly. Conventionally, the body member is provided with cam means which engages the feed pins so that the pins are moved radially in the tractor member as the tractor member rotates.
To cope with variations in width of the document to be transported, the prior art document feed devices are constructed so that the pin tractor assembly can be moved for location along the axial direction of a feed shaft. As stated in U.S. Pat. No. 2,825,559 mentioned above, the arrangement for the location includes an auxiliary shaft disposed parallel to the feed shaft, and a clamping mechanism for releasably clamping the pin tractor assembly on the auxiliary shaft at any portion thereof.
In changing the sheet size, the operator first manually releases the clamping mechanism, and slides the pin tractor assembly on the feed shaft until the feed pins engage the perforations of the sheet. In this position, the operator works the clamping mechanism again to lock the body member both axially and in its rotating direction, thereby adjusting the position of the pin tractor assembly.
According to the arrangement described above, therefore, the components used in the device are increased in number, and the construction is complicated. Also, the positioning of the pin tractor assembly is so troublesome that the operation of the device lacks in speed and accuracy.
In the device with the auxiliary shaft, in particular, the auxiliary shaft is disposed in a feed path for the sheet of material. Therefore, the device requires additional means for preventing the auxiliary shaft from interfering with the sheet. The adjustment position of the pin tractor assembly varies with the operator, possibly lowering the accuracy of the sheet feed.
As stated also in U.S. Pat. No. 2,825,559 mentioned before, moreover, the document feed device generally is provided with a sheet holding mechanism in the vicinity of the pin tractor assembly. This mechanism touches the sheet of material from above during the sheet feeding operation with the perforations of the sheet engaging the feed pins, lest the sheet be lifted or dislocated from the position for the engagement with the feed pins. Thus, the mechanism serves to regulate the sheet for stable feed. Also, the holding mechanism is adapted to be located in a closed position where it is in contact with the sheet of material during the feeding operation, and to be moved to an open position where it is separated from the sheet in removing the sheet from the feed pins.
However, the use of the extra sheet holding mechanism would result in a complicated construction of the device, higher manufacturing cost, and inefficient assembling work.
Requiring the operator's manipulation, moreover, the conventional sheet holding mechanism may possibly cause a wrong feeding operation attributed to an omission.
In fabricating the pin tractor assembly, furthermore, the feed pins generally are mounted in radially arranged feed pin bores or grooves. Since the feed pins are small-sized components independent of one another, however, the mounting work is very troublesome and inefficient.